The present invention relates to the area of hybrid transmissions for motor vehicles comprising, on the one hand, a thermal engine and, on the other hand, an electric machine.
More specifically, it has as its object a hybrid transmission for a motor vehicle equipped with a thermal engine and an electric drive machine comprising two concentric primary shafts, each supporting at least one intermediate drive on a secondary shaft connected to the wheels of the vehicle.
The principal aim of hybrid transmissions is to ensure that the kinematic drive chain of a vehicle benefits from two sources of energy, thermal and electric, of which the torque contributions may be combined in a mode known as hybrid mode, or may be used separately, either in a “pure thermal mode” in which the electric machine supplies no torque to the power train, or in a “pure electric” mode in which the thermal engine supplies no torque to the power train. Other features are also required, such as the possibility of starting the thermal engine when stationary or in motion by utilizing the electric machine as a starter, or the possibility of utilizing the electric machine as a current generator for the purpose of charging the batteries.
In its most simple design, a hybrid transmission such as that outlined above ensures the totality of the required functions for a single gear reduction ratio, that is to say without the possibility of benefiting from a plurality of forward gears, as in the case of a conventional transmission.
Disclosed in publication U.S. Pat. No. 5,433,282 is a hybrid transmission for a motor vehicle composed essentially of a simple planetary gear train, of which the three outputs, the planet gear carrier, the planet gear and the ring gear, are connected to the thermal engine, to the electric machine and to the wheels of the vehicle. The thermal engine, the electric machine and the train are coaxial. A free wheel is positioned between the thermal engine and the planetary gear of the train. In particular, this makes it possible to combine the contribution made by the electric machine and by the electric machine for the purpose of driving the vehicle, and also to provide two transmission ratios. However, the possibilities which it affords for adaptation to specific types of driving, such as typically urban driving and typically extra-urban driving in pure electric mode at moderate speeds, and typically freeway driving at high speed, for example in pure thermal mode, are limited.